Acid-BaseAcid-BaseEquilibriaEquilibria

Chapter 16Chapter 16

Modification to Syllabus

Date Sections Topics

Friday 26 Mar 17.1 – 17.2 Common-ion effect, buffered solutions

Monday 29 Mar No class Omit 17.3 – 17.5

Weds 31 Mar --- Exam #4

Acid-Base Properties of Salt Solutions

Acid Solutions:

1) Salts derived from a strong acid and a weak base.

NH4Cl (s) NH4+ (aq) + Cl- (aq)

H2O

NH4+ (aq) NH3 (aq) + H+ (aq)

2) Salts with small, highly charged metal cations (e.g. Al3+, Cr3+, and Be2+) and the conjugate base of a strong acid:

Al(H2O)6 (aq) Al(OH)(H2O)5 (aq) + H+ (aq)3+ 2+

Acid Hydrolysis of Al3+

Hydrolysis ≡ the reaction of an anion or a cation of a salt

with water

Acid-Base Properties of Salt Solutions

Neutral Solutions:

Salts derived from a strong acid and a strong base

NaCl (s) Na+ (aq) + Cl- (aq)H2O

Basic Solutions:

Salts derived from a strong base and a weak acid.

NaCH3COOH (s) Na+ (aq) + CH3COO- (aq)H2O

CH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)

CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)

CH3COO- (aq) + H2O (l) OH- (aq) + CH3COOH (aq)

At equivalence point (pH > 7):

Example of when the pH at the equivalence point of atitration will differ from 7:

Acid-Base Properties of Salts

Solutions in which both the cation and the anion hydrolyze:

• Kb for the anion > Ka for the cation, solution will be basic

• Kb for the anion < Ka for the cation, solution will be acidic

• Kb for the anion Ka for the cation, solution will be neutral

Acid-Base Behavior and Chemical Structure

Fig 16.12 Trends in acid-base properties of binary hydrides

Factors Affecting Acid Strength

Arrhenius acid - a substance that produces H+ (H3O+) in water

Brønsted acid - a proton donor

Lewis acid - a substance that can accept a pair of electrons

Lewis base - a substance that can donate a pair of electrons

Definition of An Acid

H+ H O H••••

+ OH-••••••

acid base

N H••

H

H

H+ +

acid base

N H

H

H

H+

Lewis Acids and Bases

N H••

H

H

acid base

F B

F

F

+ F B

F

F

N H

H

H

• Most general theory

• No protons donated or accepted!

• Allows treatment of a wider variety of reactionsas acid-base reactions

Coordinate covalent bond